If I search for 'c++ define for building on windows', the results do not show up.
I get the search box, and the widgets for showing how many pages of results are available.
The source for the page shows results are there, they are not just showing up.

I believe this is a Firefox bug, and I will report it there.

It looks like a problem with the code that decides to put a search box at the top of
the results. If the search box appears, then the problem occurs.

If don't want it to convert your search terms to tags, put it in quotes. It will still be hidden if the question is tagged 'windows' though. You could also choose to not hide ignored tags, which will instead give the questions a grayed out look.